This invention relates to compression release engine brakes, and more particularly to compression release engine brakes of the general type shown in Pitzi U.S. Pat. No. 5,012,778.
As is well known from such references as Cummins U.S. Pat. No. 3,220,392, compression release engine brakes operate to temporarily convert an associated internal combustion engine from a power source to a power sinking air compressor when the fuel supply to the engine is turned off and the engine brake is turned on. The engine brake operates in this way by opening an exhaust valve (or other special valve) in at least one cylinder of the engine at times when there is compressed air in the cylinder and before the engine can recover the work of compressing that air. For example, the engine brake may open an exhaust valve near the end of each compression stroke of the engine cylinder served by that exhaust valve. This releases compressed air from the cylinder and prevents the engine from recovering the work of compressing that air during the subsequent "power" stroke of the cylinder. The engine therefore absorbs and dissipates much more energy than it otherwise would, and it becomes much more effective in slowing down the vehicle in which it is installed.
In most prior art compression release engine brakes the engine exhaust valves are opened mechanically or hydraulically. In engine brakes of the type shown in the above-mentioned Cummins patent, for example, a hydraulically operated slave piston opens each exhaust valve. A hydraulic master piston actuated by another part of the engine is hydraulically connected to each slave piston. Each forward stroke of the master piston therefore produces a forward stroke of the associated slave piston which opens the associated engine exhaust valve. The engine part which actuates the master piston is selected so that the associated exhaust valve openings will have the timing required to produce good compression release engine braking. For example, the master pistons may be operated by fuel injector mechanisms or by intake or exhaust valve opening mechanisms of the same or other engine cylinders.
Because it may be difficult or even impossible to produce optimally timed compression release events using master-slave hydraulic systems of the type described above, alternatives such as those shown in Pitzi U.S. Pat. No. 5,012,778 have been devised. (The Pitzi patent is hereby incorporated by reference herein.) In Pitzi-type systems a source of hydraulic fluid at a constant, relatively high pressure is provided. A poppet-type hydraulic valve (which is "opened" by energizing an electrical coil, and which is "closed" by a return spring when the coil is no longer energized) is also provided for selectively connecting the high pressure source to a hydraulic actuator cylinder. Each time a compression release event is desired for an engine cylinder associated with the actuator cylinder, the hydraulic valve is opened by energizing its coil. The resulting application of high pressure hydraulic fluid to the actuator cylinder causes an actuator piston in that cylinder to perform a forward stroke. This opens an exhaust valve in the associated engine cylinder. After each compression release event has occurred, the hydraulic valve is "closed" by de-energizing its coil. This disconnects the actuator cylinder from the high pressure source and instead connects the actuator cylinder to a relatively low pressure hydraulic fluid sink. The piston in the hydraulic actuator is thereby enabled to perform a return stroke, which allows the engine exhaust valve to close. Because the Pitzi patent systems are electrically controlled, the system designer has greater flexibility in selecting and implementing the timing of the compression release events.
In some applications it may be advantageous to eliminate the return spring used in the Pitzi hydraulic valve. Elimination of the return spring may help reduce the electrical current and/or voltage required to operate the hydraulic valve because, when the return spring is eliminated, the electrical coil does not have to overcome the return spring force. Elimination of the return spring may also facilitate operating the hydraulic valve more rapidly and precisely, again because the force and inertia of the return spring do not have to be overcome by the electrical coil.
In view of the foregoing, it is an object of this invention to improve compression release engine brakes of the type shown in the above-mentioned Pitzi patent.
It is a more particular object of this invention to improve the type of valves used in compression release engine brakes of the type shown in the above-mentioned Pitzi patent.